Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A typical image forming apparatus such as a multi-function peripheral (MFP) and a copy-only machine includes various kinds of color conversion tables and color-adjustment functions to convert an input image into an output image for printing. However, even for an input image with a gradation in which its tone smoothly changes, converting the input image into an output image by some color tables and color-adjustment functions causes such image forming apparatus to generate an output image where tone jump or tone collapse occurs, namely an output image in which tone does not smoothly change.
There is known a method for generating an output image in which tone smoothly changes from an input image with gradation in which its tone smoothly changes. This method prepares a plurality of interpolation methods such as linear interpolation, nearest-neighbor interpolation, and spline interpolation with respect to primary colors, namely cyan, magenta, yellow, and black. Among the plurality of interpolation methods, this method decides which interpolation method is appropriate as the interpolation method relative to each of the grid points of the primary colors in a color conversion table. Then, as the interpolation method relative to each of the grid points of colors that are a secondary (or more) color in the color conversion table, this method identifies a combination of the interpolation methods for the grid points of the primary colors, which constitute the colors.